class Queue{
    constructor() {
        this.queue = []
    }
    enqueue(element) {
        this.queue.push(element)
        return element
    }
    dequeue() {
        return this.queue.shift()
    }
    front() {
        if(this.queue.length > 0) {
            return this.queue[0]
        } else {
            return undefined
        }
    }
    isEmpty() {
        return this.queue.length > 0
    }
    size() {
        return this.queue.length
    }
}